In conventional heart surgery, an incision is made in the chest, either through the sternum (a median sternotomy) or between the ribs (a thoracotomy) in order to gain access into the chest cavity. A retractor is placed in the chest incision which allows the chest bones and tissue to be spread apart to create a wide opening. Surgical instruments are then placed through this opening to perform surgery on the heart.
One of the most common types of heart surgery is coronary artery bypass grafting, or CABG. In CABG, a blockage in one or more coronary arteries is bypassed by connecting a graft vessel to the coronary artery downstream of the blockage. The technique of connecting the graft vessel to the coronary artery is known as anastomosis. The graft vessel may be a mammary artery dissected from the chest wall, wherein the upstream end of the artery is left intact and the downstream end is attached to the coronary artery. Alternatively, the graft vessel may be a section of artery or vein from elsewhere in the patient's body, or an artificial vascular graft, wherein the upstream end of the graft is attached to an artery such as the aorta, and the downstream end is connected to the coronary artery. In this way, multiple coronary artery blockages at various locations on the front, side or back of the heart may be bypassed using multiple graft vessels.
Conventionally, CABG is performed with the heart stopped, while the patient is supported on cardiopulmonary bypass, whereby the patient's blood is circulated by means of an extracorporeal pump and oxygenation system. In certain cases, however, CABG may be performed with the heart beating in a technique known as “beating heart” or “off-pump” coronary artery bypass (OPCAB), allowing cardiopulmonary bypass to be avoided. In OPCAB, the surface of the heart near the anastomosis site on the coronary artery is stabilized using a specialized instrument while the heart continues to beat. This local stabilization keeps the anastomosis site as motionless as possible while the graft vessel is connected to the coronary artery. The coronary artery is temporarily occluded or a temporary shunt is inserted into the coronary artery during the anastomosis to keep the site free of blood.
The basic functions required in an OPCAB procedure include sternal or rib retraction, heart manipulation, heart stabilization, pericardial retraction, coronary traction and hemostasis. Sternal retraction involves prying apart the opposing halves of the divided sternum to open the chest cavity. Heart manipulation entails moving, turning or lifting the heart in order to access coronary arteries on the front, back or sides of the heart. Heart stabilization is the process of stabilizing the surface of the beating heart near the anastomosis site to allow the anastomosis to be performed. Pericardial retraction is used to pull the incised pericardium out of the way for better access to the heart. Coronary retraction involves placing a suture or silastic under the coronary arteries near the anastomosis site and exerting traction on the suture or silastic so as to better expose the coronary artery. This traction may also serve to occlude the coronary artery above and below the anastomosis site to provide hemostasis. In some cases, a temporary shunt may be inserted through an arteriotomy in the coronary artery to allow blood to flow past the anastomosis site during the procedure.